1. Field of the Invention
This invention relates to a fluid pressure control device of the deceleration sensing type adapted for use in a brake system for a vehicle.
2. Description of the Prior Art
It has been known that in applying the brake in a vehicle, the braking force to be applied to the rear wheels of the vehicle must be lower by a given degree than the braking force to be applied to the front wheels because of the difference between loads by which the front and rear wheels are pushed against the surface of a road. To meet this requirement, there have been provided various fluid pressure control device such as proportioning valves. In a conventional proportioning valve, there are provided a control piston which faces input and output fluid chambers with different fluid pressure receiving areas and a control spring which exerts a spring force on this control piston in the axial direction thereof toward the input fluid chamber. The rear wheel braking fluid pressure is slowly increased at a predetermined rate by counterbalancing the force of fluid pressure with this control spring. However, the control elements include only the fluid pressure and a spring force of a given magnitude. The conventional proportioning valve, therefore, has sometimes greatly deviated from an optimum ratio in which a braking force is to be allocated to the front and rear wheels.
To solve this problem, therefore, there have been made various contrivances for making the control characteristic of the fluid pressure control device of the above stated type variable in accordance with changes in the condition of loads imposed on a vehicle. This invention is directed to an improvement also in this respect.